The technical field of this invention is radiology and, in particular, bone absorptiometry by radiographic measurements.
The depletion of bone mineral content, typically referred to as osteoporosis, is a common consequence of a variety of diseases and natural aging process. In addition to metabolic bone diseases and aging, bone minerals can be lost as the result of drugs, stress, dietary deficiencies, pregnancy or lactation. When skeletal bone mass drops below the level necessary to provide mechanical support, the depletion of bone mineral content becomes an important cause of morbidity, particularly in elderly patients.
Unfortunately, at present there are no reliable and inexpensive systems for gauging bone mineral content (BMC) with any high degree of precision, particularly during the early stages of osteoporosis or other mineral depletion disorders when dietary supplements and therapeutic agents may reverse the course of demineralization and prevent debilitating fractures or otherwise slow the progress of the disease.
Conventional methods for determining bone mineral content typically involve measurements of radiation absorption in the bone. U.S. Pat. No. 3,715,588 issued to Rose on Feb. 6, 1973, is illustrative of a prior art "bone scanner" in which a collimated X-ray beam is passed through a bone (e.g., the wrist) and detected by a radiation detector mechanically coupled to the X-ray source. The system scans back and forth across the bone to produce a complete measurement of the bone and surrounding tissue. Because of inherent differences in tissue and bone absorption, bone density (and, hence, mineral content) can be inferred from a logarithmic ratio of the intensity of radiation detected after transmission through the two media.
One problem with such scanning systems is the time required for scanning can lead to inherent blurring of the image if patient motion occurs. Additionally, the spatial resolution of conventional detectors does not permit identification of the same bone area in repeated scans. These defects lead to BMC errors on the order of five percent or more for individual patients, precluding effective use of radiographic imaging techniques for monitoring Progressive charges in bone mineral content.
There exists a need for more precise bone absorptiometry systems that can be used by the general medical community. In particular, systems which could operate to irradiate the entire image area simultaneously to form "snap shots" of the bone structure would satisfy a long-felt need in the art by greatly reducing the problem of patient motion. Moreover, higher spatial resolution systems which reduce the measurement errors associated with current bone densitometry imaging would also address an unmet need in this field.